// 设置响应头的中间件
module.exports = async(ctx, next) => {
    const contentType = 'application/json; charset=utf-8'
    ctx.set('Content-Type', contentType)
    ctx.set('Access-Control-Allow-Origin','*')
    ctx.set('Access-Control-Allow-Methods','OPTIONS,GET,PUT,POST,DELETE')
    await next()
}